1. Field of the Invention
The present invention relates to an automatic paper feeder, and more specifically, to an automatic paper feeder which is attached to an image forming machine such as an electrophotographic copying machine, and which feeds copying paper, sheet by sheet, to the image forming portion of the image forming machine.
2. Description of Related Art
This type of an automatic paper feeder, in general has a construction to raise a paper loading plate in a paper cassette in order to press the upper surface of the copying paper loaded on the paper loading plate against a paper feeding roller, and to feed the copying paper, sheet by sheet, according to the rotation of the paper feeding roller. To detect any paper jammed at the paper feeding portion, these conventional paper feeders are provided with a combination of a sensor for detecting copying paper which is provided at the downstream side of the paper feeding roller, and a timer which is set to a specified period of time from the start of the paper feeding operation and to the detection of the paper by the sensor. When the sensor does not detect the paper within the period of time preset by the timer, it is always judged that paper jamming has occurred.
Defective paper feeding includes actual paper jamming which occurs after the front end of the paper has already been fed out of the paper cassette, and no-paper feeding condition which occurs when the fed paper remains in the paper cassette or when the paper, after having moved slightly, has stopped moving before its front end reaches the paper feeding roller because of the rotation slippage of the paper feeding roller. The above mentioned no-paper feeding condition occurs when the even pressure for pressing the upper surface of the paper against the paper feeding roller is not obtained, or when the specified pressure is not obtained due to a worn paper feeding roller. The former case is the main cause of no-paper feeding condition.
However, the conventional mechanism for detecting paper jamming determines that the above described no-paper feeding condition is a paper jamming, then stops the copying operation and displays a paper jamming alarm on the operation panel. Therefore, the operator must always check the automatic paper feeder for jammed paper before restarting the operation. This procedure is complicated and, at the same time, time-consuming.